In the operation of lasers, especially those emitting non-visible beams, it is important to know when the laser starts to generate laser beams, that is the threshold of lasing action. Also, it is desirable to determine the nature of lasing action, location of the beam for alignment of optical components and the radial profile of the beam. In the prior art, this was done haphazardly and with what was available, such as a black exposed "Polaroid" type film, which comprises a black film mounted on a white backing material. When the exposed black film was placed in the beam path, the beam would vaporize or burn off areas of the black film whereat the laser beam would impinge. An outline of the beam's cross-section or profile would thus appear on the film backing as a burned region.
Although this generally used method is inexpensive, there is a substantial deficiency and disadvantage, namely, that when the laser beam burns off the black material, the film is vaporized and smoke particles are ejected into the atmosphere. When the beam hits the black material, there is a popping noise and smoke is generated. Thus, there is a visual and audio indication that a laser beam is being generated. The particles fly about, and in many cases, fall unto the optical surfaces of the laser apparatus. Although the particles may be small, over a period of time, there is an accumulation of particles and the optical devices are damaged by the high power laser beam concentrating energy at the contaminated spots.